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Wednesday 30th warm but overcast with rain in the afternoon.
Having spent the entire day discussing different ideas about zenith boards, shutters and external slides I have scrapped the whole idea.
I need to put the slides on the inside of a thick, laminated, dome profile board. The slides must be placed at such a height that they safely clear the dome on each side of the observation slit. This way I can achieve the lowest possible profile for the shutters. So that they don't catch the wind.
The second image shows the [roughly propped up] shutters from the rear of the dome. The shutters are spherical and an exact copy of the dome profile. So I think they can go lower than this. Their curvature and lateral movement, to open, favours clearance from the dome.
A thick, external, laminated, plywood profile, above the dome, would provide increased beam stiffness in conjunction with that below. This will help to support the weight of the shutters and avoid dome flexure. Failing that I shall have to seriously consider metal reinforcement.
After further thought I will have to use aluminium to reinforce the upper and lower zenith boards. The depth isn't sufficient for plywood to do much more than flex and add weight. There has to be a compromise between beam depth and shutter projection.
Since the loads are mostly downwards the upper structure dominates in beam stiffness. This is the case even if the two layers are bolted in a sandwich over the dome material. The slit facing, zenith board should be full depth and in 10mm thick, aluminium sheet.
Laminated ply spacers, above and below the dome, will help to spread the loads. With matching, aluminium profiles at the rear. Through [eye] bolting will then enjoy solid resistance. Rather than directly crushing a narrow section of laminated ply. Vertical bolts will compress these sandwiches onto the dome material.
Now I need to make some mock-ups. To see how much clearance I need for the slides and shutters to clear the dome.
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